Biodesulfurization of hydrocarbons

ABSTRACT

A process for converting organic sulfur compounds contained in liquid hydrocarbons to elemental sulfur. The liquid hydrocarbons are solubilized in an organic solvent and reacted in the presence of a biocatalyst and hydrogen. The organic solvent is a nucleophilic solvent having a pK a  greater than about 2, an electrophilic solvent having a pK a  more negative than about −2, or mixtures thereof. The biocatalyst may be supported on a Lewis acid. Elemental sulfur is removed from the liquid hydrocarbons. Liquid hydrocarbons treated in accordance with this process have significantly reduced concentrations of organic sulfur compounds and thus reduced viscosity.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a process for removing organicsulfur compounds from hydrocarbons, and more particularly, to a processfor converting organic sulfur compounds that are contained in a liquidhydrocarbon, to elemental sulfur by contacting the hydrocarbon with anorganic solvent and hydrogen in the presence of a biocatalyst andthereafter removing the elemental sulfur.

[0003] 2. Description of Related Art

[0004] Many crude oils that are produced from subterranean environs,transported via tubulars, such as pipelines, risers, casing and tubing,and ultimately refined contain organic sulfur compounds. These processesare interfered with and/or complicated due to the corrosive nature andthe high viscosity of such sulfur compounds, especially heterocyclicsulfur compounds, and the fouling of catalyst utilized in petroleumrefining that is attributable to such sulfur compounds. Further, manycountries have enacted legislation reducing the amount of sulfur thatmay be present in gasoline and other fuels refined from crude oil in anattempt to reduce sulfur emissions to the atmosphere from burning suchfossil fuels. As worldwide reserves of clean burning, low sulfurhydrocarbons are increasingly being depleted, attention has turned tofinding methods of reducing the sulfur content of lower grade,relatively high sulfur containing crude oils so as to facilitate thetransportation and refining thereof.

[0005] One method that has been proposed involves the use of abiocatalyst that alters the sulfur-bearing heterocycles in crude oil bycleaving carbon-sulfur bonds and/or joining polar substituents to thesulfur heteroatom and/or the hydrocarbon framework. In this manner, theviscosity and the sulfur content of the crude oil is reduced and thesulfur is converted to elemental sulfur and/or hydrogen sulfide whichcan be more easily separated from crude oil. This method generallyinvolves reacting a crude oil with a biocatalyst in the presence of anaqueous solvent and hydrogen. Recently, it has been proposed to utilizean organic solvent, such as dimethylformamide (DMF) as an organicsolvent in this method. However, rates of biodesulfurization using suchan organic solvent are quite slow, especially for relatively highmolecular weight crude oil molecules. Thus, a need exists for processfor desulfurizing crude oil using an organic solvent and a biocatalystthat results in relatively high rates of sulfur conversion.

SUMMARY OF THE INVENTION

[0006] To achieve the foregoing and other objects, and in accordancewith the purposes of the present invention, as embodied and broadlydescribed herein, one characterization of the present invention is aprocess for converting organic sulfur compounds contained in liquidhydrocarbons. This process comprises reacting organic sulfur compoundscontained in liquid hydrocarbons in the presence of a biocatalyst,hydrogen and an organic solvent thereby converting the organic sulfurcompounds to elemental sulfur. The organic solvent is selected from thegroup consisting of a nucleophilic solvent having a pK_(a) greater thanabout 2, an electrophilic solvent having a pK_(a) more negative thanabout −2, or mixtures thereof.

[0007] In another characterization of the present invention, a processis provided for removing organic sulfur compounds from liquidhydrocarbons. The process comprises a) contacting liquid hydrocarbonscontaining organic sulfur compounds with an organic solvent, saidsolvent solubilizing said liquid hydrocarbons, and b) reacting theliquid hydrocarbons that are solubilized in the organic solvent in thepresence of a biocatalyst and hydrogen thereby converting the organicsulfur compounds to elemental sulfur. The organic solvent is selectedfrom the group consisting of a nucleophilic solvent having a pK_(a)greater than about 2, an electrophilic solvent having a pK_(a) morenegative than about −2, or mixtures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The accompanying drawings, which are incorporated in and form apart of the specification, illustrate the embodiments of the presentinvention and, together with the description, serve to explain theprinciples of the invention.

[0009] In the drawings:

[0010]FIG. 1 is a schematic flow diagram of one embodiment of theprocess of the present invention;

[0011]FIG. 2 is a schematic flow diagram of another embodiment of theprocess of the present invention;

[0012]FIG. 3 is a graph that depicts the boiling point distribution forcrude oil desulfurized in a slurry of organic solvent (N-buytlamine) andbiocatalyst as a function of the amount of crude oil distilled;

[0013]FIG. 4 is a graph that depicts the boiling point temperature forcrude oil desulfurized in a slurry of organic solvent (methyl ethylketone) and biocatalyst as a function of the amount of crude oildistilled;

[0014]FIG. 5 is a graph that depicts the conversion rate of organicsulfur initially present in a crude oil to elemental sulfur in thepresence of a biocatalyst as a function of solvent nature (pK_(a));

[0015]FIG. 6 is a graph that depicts the crude oil viscosity as afunction of the organic to elemental sulfur conversion;

[0016]FIG. 7 is a graph that depicts the amount of organic sulfurinitially present in a crude oil that is converted in the presence of abiocatalyst to elemental sulfur as a function of the amount ofbiocatalyst that is immobilized on a support; and

[0017]FIG. 8 is a graph that depicts the amount of elemental sulfurremoved by using a solvent/crude oil mixture with water as a function ofthe molar ratio of wash water to solvent.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] In accordance with one embodiment of the present invention, anucleophilic and/or electrophilic organic solvent(s) is introduced vialine or conduit 5 into a hydrocarbon stream, for example crude oil,heavy crude oil, bitumen, or a refined fraction of crude oil, which istransported in line or conduit 1. The hydrocarbon stream issubstantially completely solubilized in the organic solvent. Hydrogengas from any suitable source (not illustrated) is also introduced vialine or conduit 3 into the mixture of the hydrocarbon stream in organicsolvent in line 1. The resultant mixture of hydrocarbon, organic solventand hydrogen is transported via line 1 into or near the bottom of areactor 10. Reactor 10 contains a packed bed 12 of biocatalyst dispersedon a support. The biocatalyst used in accordance with the presentinvention is a microorganism such as that available from FinnertyEnterprises Inc., Athens, Ga. In reactor 10, organic sulfur compoundsthat are present in the hydrocarbon stream are converted into elementalsulfur at a temperature of less than about 165° F. While not wishing tobe bound by any particular mechanism or theory and although notcompletely understood, the conversion of organic sulfur compounds toelemental sulfur in the reactor is believed to occur in accordance withtwo overall chemical mechanisms wherein R₁, R₂, R₃, and R₄ representhydrocarbon constituents. Organic sulfides are converted in accordancewith reaction A and organic thiophenes are converted in accordance withreaction B.

R₁S R₂+H₂→R₁H+R₂H+S  (A)

[0019]

[0020] The organic solvent having treated hydrocarbons solubilizedtherein and elemental sulfur is removed from reactor 10 via line orconduit 16 and is introduced into the lower end of contactor 20 andcounter currently contacted with wash water from any suitable source(not illustrated). The wash water is introduced into contactor 20 vialine or conduit 24 in an amount of from about 10 to about 20 moles ofwash water per mole of solvent. The organic solvent and elemental sulfurare solubilized in the wash water. The treated hydrocarbons having areduced sulfur content are removed from contactor 20 via line 26 fortransportation and/or further processing. This solution is removed fromcontactor 20 via line or conduit 22 and transported to distillationvessel 30 wherein the solution is heated to separate the organic solventin the form of vapor from a remaining water and sulfur slurry. Thevaporous solvent is removed from distillation vessel 30 via line orconduit 5 and cools and condenses to liquid form while being recycled inline 5 for introduction into the feed hydrocarbon stream as previouslydiscussed. The aqueous sulfur slurry is removed from distillation vessel30 via line 32 and introduced into a separator 40 wherein sulfur iseither phase separated or filtered from the water, heated and removed asa liquid product via line or conduit 42. The water is then recycled vialine or conduit 24 to contactor 20.

[0021] In accordance with another embodiment of the process of thepresent invention as illustrated in FIG. 2, a stirred tank reactor 80 isutilized in lieu of packed bed reactor 10. Biocatalyst is introduced vialine or conduit 92 into the mixture of hydrocarbon, organic solvent andhydrogen that is introduced via line 1 into reactor 80. Reactor 80 isprovided with any suitable means, such as a rotating blade 82, tomaintain a substantially uniform dispersion of biocatalyst, hydrocarbon,organic solvent and hydrogen in reactor 80. The reacted mixture istransported via line 16 from reactor 80 to settler 90 wherein thebiocatalyst is separated from the mixture and returned to reactor 80 vialine 92, pump 94 and line 1. The organic solvent having treatedhydrocarbons solubilized therein and elemental sulfur is thentransported via line 96 and introduced into the lower end of contactor20 for processing as described with respect to FIG. 1.

[0022] In accordance with the present invention, applicant hasdiscovered that utilizing certain organic solvent(s), which has beenselected in accordance with parameters set forth below, unexpectedlyresults in very high conversions of organic sulfur compounds toelemental sulfur in extremely short periods of time.

[0023] The organic solvent utilized in the process of the presentinvention is an electron donating solvent, i.e. nucleophilic or basic,an electron accepting solvent, i.e. electrophilic or acidic, or acombination thereof. It is believed that nucleophilic solvents catalyzeorganic sulfur conversion in accordance with reaction A above, whileelectrophilic solvents catalyze organic sulfur conversion that occurs inaccordance with reaction B above. Thus, where the hydrocarbon liquid tobe treated contains primarily organic sulfides, a nucleophilic solventshould be employed in the process of the present invention. Where theliquid hydrocarbon to be treated contains primarily organic thiopenes, aelectrophilic solvent should be used. The relative nature of anelectrophilic or nucleophilic solvent is noted by the equilibriumconstant (pK_(a)) of a given solvent. As is evident to a skilledartisan, pK_(a) values for a given solvent are typically obtained froman authoratative text, for example “Organic Solvents: PhysicalProperties and Methods of Purification”, John A. Riddick and William B.Bunger, published by Wiley Interscience (3rd edition; 1970). Fornucleophilic solvents, the pK_(a) increases in the positive directionfrom a value of 0 with increasing electron donating capability. Forelectrophilic solvents, the pK_(a) decreases from a value of 0 withincreasing electron accepting capability. Nucleophilic solvents suitablefor use in accordance with the process of the present invention arethose having a pK_(a) value greater than about 2, more particularlygreater than about 6 and most particularly greater than about 10, whileelectrophilic solvents suitable for use in accordance with the processof the present invention are those having a pK_(a) value more negativethan about −2, more particularly more negative than about −6 and mostparticularly more negative than about −10. Suitable nucleophilicsolvents include N-butylamine, diethylamine, butanediamine,ethylenimine, toluene, pyridine, aniline and acetophenone, whilesuitable electrophilic solvents include methylethylketone, pyrrole,benzaldehyde.

[0024] Where the liquid hydrocarbon to be treated contains both organicsulfides and thiopenes in significant quantities, a combination ofnucleophilic and electrophilic solvents that are selected in accordancewith the parameters outlined herein may be employed in the process ofthe present invention. In such instances, it is also suitable to use anamphiprotic solvent, i.e. a solvent that contains both electron donatingand electron accepting groups in one solvent molecule. An example of anamphiprotic solvent is ethanolamine. One potential disadvantage withemploying both an amphiprotic solvent or a nucleophilic solvent and anelectrophilic solvent is the potential for these solvents to exchangeelectrons between each other thus reducing their effectiveness inconverting organic sulfur compounds. Accordingly, in such instances, itis preferred to use a nucleophilic solvent in conjunction with a Lewisacidic support for the biocatalyst, such as that commercially availablefrom Alcoa Industrial Chemicals under the trade name designation HiQAlumina® and DD2. It is believed that the acid support catalyzesreaction B thereby increasing the rate of conversion of organicthiopenes. The support should be selected to have a relatively highdegree of Lewis acidity.

[0025] It will be evident to a skilled artisan that conversion oforganic sulfides and/or thiopenes to elemental sulfur in accordance withthe process of the present invention concomitantly results in viscosityreduction of the treated liquid hydrocarbon which assists in thetransportation and further treatment of such liquid hydrocarbon.

[0026] The following examples demonstrate the practice and utility ofthe present invention, but are not to be construed as limiting the scopethereof.

EXAMPLE 1

[0027] A crude oil produced from the Oregon Basin field in Wyoming wascombined with N-butylamine solvent and a biocayalyst (from FinnertyEnterprises Inc., Athens, Ga.) and desulfurized in a slurry reactor at atemperature of 158° F. for a period of one hour. Hydrogen gas wassupplied to the reactor at a partial pressure of 1200 to 1400 psig. Theconcentration of the biocatalyst was 3.75 wt % of the crude oil and theconcentration of crude oil in the solvent was 40 wt %. The reactantslurry was removed from the reactor and the biocatalyst was separatedfrom the slurry by centrifugation. The treated crude oil was washed withwater to remove the solvent and elemental sulfur and then distilled. Avirgin sample of the Oregon Basin crude oil was also distilled forcomparative purposes. As evident from the results of this distillationthat are illustrated in FIG. 3, significant increases in the boilingpoint distribution data, as compared to the virgin crude oil, wereobtained, i.e. larger amounts of product components were distilled forany given boiling point. The largest increase occurred for the toluenecomponent of crude oil, i.e. 231° F. It is believed that nucleophilicsolvents, e.g. N-butylamine, make the biocatalyst pore wall moreelectronegative, thus catalyzing reaction A and yielding lower boilingR₁H and R₂H components, e.g. toluene being an R₁H or R₂H component.

EXAMPLE 2

[0028] A crude oil produced from the Oregon Basin field in Wyoming (sameas Example 1) was combined with methyl ethyl ketone (solvent) and abiocatalyst (from Finnerty Enterprises Inc., Athens, Ga.) anddesulfurized in a slurry reactor at a temperature of 72-75° F. for aperiod of two and one half hours. Hydrogen gas was supplied to thereactor at a partial pressure of 1200 to 1400 psig. The concentration ofthe biocatalyst was 2.10 wt % of the crude oil and the concentration ofcrude oil in the solvent was 40 wt %. The reactant slurry was removedfrom the reactor and the biocatalyst was separated from the slurry bycentrifugation. The treated crude oil was washed with water to removethe solvent and elemental sulfur and then distilled. A virgin sample ofthe Oregon Basin crude oil was also distilled for comparative purposes.As evident from the results of this distillation which are illustratedin FIG. 4, an electrophilic solvent, e.g. methyl ethyl ketone, did notyield any significant change in the boiling point distribution data,i.e. substantially equal amounts of product components were distilledfor any given boiling point. This result would be expected for reactionB where component molecular weights are not significantly changed due tothe reaction.

EXAMPLE 3

[0029] A crude oil produced from the Oregon Basin field in Wyoming (sameas use in Examples 1 and 2) was combined with a solvent and abiocatalyst (from Finnerty Enterprises Inc., Athens, Ga.) anddesulfurized in a slurry reactor at a temperature of 158-165° F. for aperiod varying from 0.8 to 2.3 hours depending upon the run. Hydrogengas was supplied to the reactor at a partial pressure of 1200 to 1400psig. The concentration of the biocatalyst was 2.10 wt % of the crudeoil and the concentration of crude oil in the solvent was 40 wt %. Thereactant slurry was removed from the reactor and the biocatalyst wasseparated from the slurry by centrifugation. The treated crude oil waswashed with water to remove the solvent and elemental sulfur. Theconversion rate of organic sulfur to elemental sulfur was measured usingX-ray and differential scanning colorimetry techniques. This procedurewas repeated using four different solvents. One solvent, methyl ethylketone (MEK) is electrophilic, two solvents, pyridine (PY) andN-butylamine (NBA), are nucleophilic and a fourth solvent, a 50/50 blendof NBA and MEK, has a nucleophilic nature. This procedure was alsorepeated without using a solvent. The results of these reactions, whichare graphically illustrated in FIG. 5, indicate that the greater theelectrophilic nature (−pK_(a) value) or the nucleophilic nature (+pK_(a)value) of the organic solvent utilized in the process of the presentinvention, the greater the rates of conversion of organic sulfur that isobtained. Acceptable rates of conversion are those greater than about0.01 hr⁻¹.

EXAMPLE 4

[0030] A crude oil produced from the Oregon Basin field in Wyoming wascombined with a solvent and a biocatalyst (from Finnerty EnterprisesInc., Athens, Ga.) and desulfurized in a slurry reactor at a temperatureof 72-75° F. for a period of 1.0 to 2.5 hours depending upon the run.Hydrogen gas was supplied to the reactor at a partial pressure of 1200to 1400 psig. The concentration of the biocatalyst was 2.10 wt % of thecrude oil and the concentration of the crude oil in the solvent was 40%.The reactant slurry was removed from the reactor and the biocatalyst wasseparated from the slurry by centrifugation. The treated crude oil waswashed with water to remove the solvent and elemental sulfur. Thepercentage of organic sulfur converted to elemental sulfur was measuredusing x-ray and differential scanning colorimetry techniques. Theviscosity of the desulfurized crude oil was also measured by a capillaryflow tube technique. This procedure was repeated using N-butylamine andmethyl ethyl ketone as the solvent and without using a solvent. Theresults are plotted in FIG. 6. It is evident from these results that theviscosity reduction achieved from desulfurizing crude oil in accordancewith the process of the present invention is independent of whether anucleophilic or electrophilic solvent is employed.

EXAMPLE 5

[0031] A crude oil produced from the Oregon Basin field in Wyoming wascombined with N-butylamine solvent and fed to a reactor packed with abiocatalyst dispersed on a support. The biocatalyst was from FinnertyEnterprises Inc., Athens, Ga. Two separate catalyst supports were usedin different runs. One support was a 50/50 weight percentage blend of ahigh Lewis acidity support available under the trade name designationHiQ®-7219CC and a lower Lewis acidity support available under the tradename designation DD2 from Alcoa Industrial Chemicals. The other supportwas consisted entirely of the DD2 low Lewis acidity support. The crudeand solvent resided in the packed bed reactor at 145-150° C. for aperiod of from 0.5 to 2 hours. Hydrogen gas was supplied to the reactorat a partial pressure of 541 to 1383 psig. The concentration of thebiocatalyst was 21.1 wt % of the total catalyst and support weight whenthe blended HiQ®/DD2 support was utilized and 16.7 wt % of the totalcatalyst and support weight when the DD2 support was used. The treatedcrude oil was removed from the reactor and washed with water to removethe solvent and elemental sulfur. The percentage of organic sulfurconverted to elemental sulfur was measured using x-ray and differentialscanning colorimetry techniques. This procedure was repeated using acatalyst which was employed in previous runs, using a differentcatalyst, or using a different catalyst support. As clearly indicated bythe results that are illustrated in FIG. 7, using a catalyst having ahigher Lewis acidity support resulted in significant increases inorganic sulfur conversion. In addition, using higher catalystconcentrations increased organic to elemental sulfur conversion.Parameters not effecting organic sulfur conversion were crude oilconcentration in the solvent, hydrogen partial pressure and residencetime.

EXAMPLE 6

[0032] Samples of an Oregon Basin crude oil that was desulfurized inaccordance with the present invention using butanediamine (BDA) orethanolamine (EA) as the organic solvent were washed at 70-75° F. toremove solvent and elemental sulfur therefrom. The molar ratio of waterto solvent present in the desulfurized crude was varied in differentruns to determine the effect thereof. As illustrated by the results inFIG. 8, a molar ratio of between about 10 to about 20 moles of washwater per mole of solvent resulted in the greatest amount of elementalsulfur being removed from the desulfurized crude oil. In accordance withthe present invention, use of organic solvents with two polar functions,such as BDA or EA, result in greater amounts of elemental sulfur beingremoved from the desulfurized crude oil than use of mono polar solvents,such as NBA or MEK.

[0033] While the foregoing preferred embodiments of the invention havebeen described and shown, it is understood that the alternatives andmodifications, such as those suggested and others, may be made theretoand fall within the scope of the invention.

I claim:
 1. A process for converting organic sulfur compounds containedin liquid hydrocarbons comprising: reacting organic sulfur compoundscontained in liquid hydrocarbons in the presence of a biocatalyst,hydrogen and an organic solvent selected from the group consisting of anucleophilic solvent having a pK_(a) greater than about 2, anelectrophilic solvent having a pK_(a) more negative than about −2, ormixtures thereof thereby converting said organic sulfur compounds toelemental sulfur.
 2. The process of claim 1 wherein said nucleophilicsolvent has a pK_(a) greater than about
 6. 3. The process of claim 1wherein said nucleophilic solvent has a pK_(a) greater than about
 10. 4.The process of claim 1 wherein said sulfur compounds are sulfides andsaid organic solvent is N-butylamine.
 5. The process of claim 1 whereinsaid step of reacting is performed at a temperature of about 165° F. orless.
 6. The process of claim 1 wherein said electrophilic solvent has apK_(a) more negative than about −6.
 7. The process of claim 1 whereinsaid electrophilic solvent has a pKa more negative than about −10. 8.The process of claim 1 wherein said sulfur compounds are thiopenes andsaid organic solvent is methylethylketone.
 9. The process of claim 1wherein said biocatalyst is dispersed on a support.
 10. The process ofclaim 9 wherein said support exhibits Lewis acidity.
 11. A process forremoving organic sulfur compounds from liquid hydrocarbons comprising:a) contacting liquid hydrocarbons containing organic sulfur compoundswith an organic solvent, said solvent solubilizing said liquidhydrocarbons and being selected from the group consisting of anucleophilic solvent having a pK_(a) greater than about 2, anelectrophilic solvent having a pK_(a) more negative than about −2, ormixtures thereof; b) reacting said liquid hydrocarbons that aresolubilized in said organic solvent in the presence of a biocatalyst andhydrogen thereby converting said organic sulfur compounds to elementalsulfur.
 12. The process of claim 11 further comprising: c) contactingsaid organic solvent and said liquid hydrocarbons after the step ofreacting with water thereby solubilizing said elemental sulfur and saidorganic solvent into said water.
 13. The process of claim 12 whereinsaid organic solvent and said liquid hydrocarbons are contacted withbetween about 10 to about 20 moles of said water per mole of saidorganic solvent.
 14. The process of claim 12 further comprising: d)removing said organic solvent from said water and said elemental sulfur;and e) recycling said organic solvent to step a).
 15. The process ofclaim 14 further comprising: f) separating said sulfur from said water;and g) recycling said water from which said sulfur is separated to stepc).
 16. The process of claim 11 wherein said nucleophilic solvent has apK_(a) greater than about
 6. 17. The process of claim 11 wherein saidnucleophilic solvent has a pK_(a) greater than about
 10. 18. The processof claim 11 wherein said sulfur compounds are sulfides and said organicsolvent is N-butylamine.
 19. The process of claim 11 wherein said stepof reacting is performed at a temperature of about 165° F. or less. 20.The process of claim 11 wherein said electrophilic solvent has a pK_(a)more negative than about −6.
 21. The process of claim 11 wherein saidelectrophilic solvent has a pK_(a) more negative than about −10.
 22. Theprocess of claim 11 wherein said sulfur compounds are thiopenes and saidorganic solvent is methylethylketone.
 23. The process of claim 11wherein said biocatalyst is dispersed on a support.
 24. The process ofclaim 23 wherein said support is a Lewis acid.
 25. The process of claim11 wherein said liquid hydrocarbons are crude oils.